Criteria for Sustainable Disposal of Sewage Sludge

MIDDLE POMERANIAN SCIENTIFIC SOCIETY OF THE ENVIRONMENT PROTECTION
ŚRODKOWO-POMORSKIE TOWARZYSTWO NAUKOWE OCHRONY ŚRODOWISKA
Annual Set The Environment Protection
Rocznik Ochrona Środowiska
Volume/Tom 17. Year/Rok 2015
ISSN 1506-218X
337–350
Criteria for Sustainable Disposal of Sewage Sludge
Aneta Czechowska-Kosacka*, Yucheng Cao**, Artur Pawłowski*
*
Lublin University of Technology, Poland,
**
Zhejing Agriculture and Forestry University, Hagzhou, China
1. Introduction
Phosphorus and potassium compounds are considered important
for plant growth. What is more, food production for a growing number of
people depends on their availability. Phosphorus and potassium compounds are delivered to soil as salts obtained from mineral deposits. The
problem is that mineral resources are quickly exhausted and this threatens the fundamental paradigm of sustainable development stating that
providing the currently living generations with the essential livelihoods
will not deprive future generations of the ability to satisfy their own
needs [2,6–8,19,21,22]. This paradigm necessitates reducing the exploitation of natural reserves of phosphorus and potassium. The search for other sources of these compounds draws attention to sewage sludge produced in sewage treatment plants.
The sludge contains about 3.2% of phosphorus and 0.4% of potassium. Their reimplementation into soil, after appropriate treatment,
may significantly reduce the consumption of natural reserves of phosphorus and potassium.
Sewage sludge contains multiple compounds having agriculture
values, including organic matter, nitrogen, phosphorus and potassium
compounds and, to a lesser extent, calcium, sulphur and magnesium
compounds.
Addition of sewage sludge to land increases organic matter in the
soil. The organic matter improves the physical, chemical, biological and
biochemical properties of soil. Sewage sludge contains high levels of
338
Aneta Czechowska-Kosacka, Yucheng Cao, Artur Pawłowski
organic matter which is beneficial to the physical, chemical and biological properties of soil. Organic matter improves the physical quality of
soil and the root environment by increasing the soil water retentioncapacity and improving soil aggregation and by reducing soil bulk density (see
table 1).
The improved physical properties of soil and high levels of organic matter can enhance biological properties in the soil, including improvement of enzymatic, microbial and earthworm activities.
Table 1. Physical properties of soil improved by the use of sewage sludge [16]
Tabela 1. Fizyczne właściwości gleby wzbogaconej osadami ściekowymi [16]
Crop land
Forest land
Turfgrass
Experimental
period (a)
Decrease in
bulk density
Increase in
porosity
2~3
1
1
18
4.1
5.67~35.5
12.9
2.0~3.5
9.7~10.1
Increase in
water
holding
capacity
4.9
8~16
29~580
On the other hand, sewage sludge also contains an array of unfavourable substances, including (1) metallic pollutants, such as zinc, copper, nickel, cadmium, lead, mercury, and chromium, (2) persistent organic pollutants, such as organochlorine pesticides and polychlorinated biphenyls (PCBs), and (3) microorganism pollutants, such as pathogens
[4,5,7]. Content of those pollutants requires careful treatment and disposal of sewage sludge.
Untreated sewage sludge also contains micro-organisms that pose
health risks. Therefore, sewage sludge should be treated prior to use, in
order to decrease the water content and to eliminate odours and diseasecausing agents. Typical sludge treatment includes thickening, dewatering,
drying and stabilization (e.g. anaerobic digestion and alkaline stabilization). In general, these unit operations take place on-site (at WWPTs) and
require a large amount of energy, depending on the specific process used.
After on-site treatment, sewage sludge is normally transported
off-site for safe disposal or agricultural use. Currently, in majority of
countries, land application and landfilling are the most often used sewage
339
Criteria for Sustainable Disposal of Sewage Sludge
sludge disposal methods, although there are some alternatives (e.g. incineration and pyrolysis) that have been well developed [11–14]. Landfill
disposal can be regarded as the least favourable, and the most unsustainable because of the following factors:
 it commonly generates undesired emissions (e.g. leachate, landfill gas
and odours) to water, air and soil,
 valuable nutrient substances (e.g. compounds of N and P) contained in
sludge are wasted and become pollutants, mostly presented in leachate.
For safe management of sewage sludge it is necessary to follow
strict regulations.
Therefore, regulations related to the land application of sewage
sludge in EU. USA, China and Poland will be characterized.
Typical composition of sewage sludge is presented in Table 2.
Table 2. Typical chemical composition and properties of primary, activated and
digested sludge [10]
Tabela 2. Typowy skład chemiczny i właściwości osadów surowych, czynnych
i przefermentowanych
Total dry solids
(TS), %
Volatile solids
(% of TS)
Grease and fats
(% of TS)
Ether soluble
Ether extract
Protein (% of TS)
Nitrogen (N, %
of TS)
Primary sludge
Digested sludge
Range
Typical
Range
Typical
Activated
sludge
Range
2.0–8.0
5.0
6–12
10
0.83–1.16
60–80
65
30–60
40
59–88
5–20
18
6–30
7–35
20–30
25
15–20
18
1.5–4
2.5
1.6–6
3
5–12
2.4–5
340
Aneta Czechowska-Kosacka, Yucheng Cao, Artur Pawłowski
Table 2. cont.
Tabela 2. cd.
Phosphorous
(P2O5, % of TS)
Potash (K2O, %
of TS)
Cellulose (% of
TS)
Iron
(not as sulphide)
Silica (SiO2, %
of TS)
Alkalinity
(kg/l as CaCO3)
Organic acids
(kg/l as Hac)
Energy content
(MJ/kg)
Primary sludge
Digested sludge
Range
Typical
Range
Typical
Activated
sludge
Range
0.8–2.8
1.6
1.5–4
2.5
2.8–11
0–1
0.4
0–3
1
0.5–0.7
8–15
10
8–15
10
2–4
2.5
3–8
4
15–20
10–20
0.5–1.5
0.6
2.5–3.5
0.58–1.1
0.2–2
0.5
0–0.6
3
1.1–1.7
23–29
25
9–14
12
19–23
2. Criteria for the European Union
As early as 1986, the Council of the European Union promulgated
the Directive: “on the protection of the environment, and in particular of
the soil, when sewage sludge is used in agriculture (86/278/EEC)” [1].
The aim of the Directive is to regulate the use of sewage sludge in agriculture in such a way as to prevent harmful effects on soil, vegetation,
animals and people, while encouraging its proper use. To this end, it sets
out the requirements regarding pollutant limits, operational standards,
management practices, sampling and analysis methods, recordkeeping
(e.g. the quantities and properties of sludge produced) and, periodical
reporting. The Directive prohibits the use of untreated sludge on agricultural land unless it is injected into the soil under specific conditions.
Criteria for Sustainable Disposal of Sewage Sludge
341
Directive sets limit values for seven heavy metals (cadmium,
copper, nickel, lead, zinc, mercury and chromium), both in soil and in
sludge itself. It describes limit values for concentrations of heavy metals
in soil to which sludge is applied, concentrations of heavy metals in
sludge, and the maximum annual quantities of such heavy metals which
may be introduced into soil (Tables 3, 4 and 5).
Table 3. Limit values for concentrations of heavy metals in soil [1]
Tabela 3. Dopuszczalne stężenia metali ciężkich w glebie [1]
Metals
Cadmium
Copper
Nickel
Lead
Zinc
Mercury
Chromium
mg/kg of dry matter
1 to 3
50 to 140
30 to 75
50 to 300
150 to 300
1 to 1.5
–
Table 4. Limit values for heavy-metal concentrations in sludge used in
agriculture [1]
Tabela 4. Dopuszczalne stężenia metali ciężkich w osadach ściekowych
wykorzystywanych w rolnictwie [1]
Metals
Cadmium
Copper
Nickel
Lead
Zinc
Mercury
Chromium
mg/kg of dry matter
20 to 40
1 000 to 1 750
300 to 400
750 to 1 200
2 500 to 4 000
16 to 25
–
342
Aneta Czechowska-Kosacka, Yucheng Cao, Artur Pawłowski
Table 5. Limit values for amounts of heavy metals which may be added
annually to agricultural land, based on a 10-year average [1]
Tabela 5. Dopuszczalne stężenia metali ciężkich, jakie można wprowadzać
w ciągu roku do gleby, w oparciu o 10-letnią średnią [1]
Metals
Cadmium
Copper
Nickel
Lead
Zinc
Mercury
Chromium
kg/ha/yr
0.15
12
3
15
30
0.1
–
The current Sewage Sludge Directive addresses both pathogen reduction and the potential for accumulation of persistent pollutants in soils
but sets no limits for organic contaminants. The Directive establishes
limit values for seven heavy metals (cadmium, copper, nickel, lead, zinc,
mercury and chromium), both in soil and in sludge itself. It specifies
general land use, harvesting and grazing restrictions to provide protection
against health risks from residual pathogens. The Directive requires all
sludge to be treated before being applied to agricultural land, but allows
the injection of untreated sludge into the soil under specific conditions.
While it calls for the use of treated sludge, the Directive does not specify
treatment processes.
The Member States can apply stricter restrictions than those determined in Directive 86/278/ EEC and this is observed in several cases.
Specifically, 16 out of the 27 EU countries have set more rigorous national standards for heavy metals concentrations in sludge, whereas 10
out of 27 countries have set stricter limit values for the concentrations of
heavy metals in soil. There is a wide variation in national limit values for
heavy metals, even between similar geographical areas, such as the Nordic or Baltic countries. Nordic countries (Finland, Sweden, Denmark and
Netherlands) have set the lowest limit values. On the other hand, except
of France, Malta and Slovenia, Mediterranean countries have adopted the
limit values proposed by the EU Directive.
Criteria for Sustainable Disposal of Sewage Sludge
343
Apart from heavy metals included in the EU Directive 86/278,
several countries have set limit values for chromium as well as for other
categories of pollutants commonly detected in sludge such as pathogens
and organic micropollutants. Limit values for total chromium in sludge
have been set by 19 out of the 27 countries, while different legislation on
this matter is observed in different parts of Belgium. The limit values of
total Cr range from 40 mg/kg dry matter (Slovenia) to 1750 mg/kg dry
matter (Luxembourg).
So far, except for Hungary which has set a limit value of 1 mg/kg
for Cr(VI), no limit values have been set for this chromium species by
other European countries, despite the fact that it is much more toxic than
total chromium [18].
3. Criteria for the USA
The US EPA introduced regulations in 1993 [9,17] that established minimum standards that must be met if sludges are to be landapplied. The regulations include concentration limits for nine metals and
for pathogens, and requirements for the reduction of flies and rodents
attraction. The regulations establish Class A sludges, which have been
treated to total elimination of pathogens (disease-causing organisms), and
Class B, in which pathogens have been reduced but are still present. Under the federal 503 rules certain site restrictions apply to Class B use, but
no individual site permits are required for its use.
The federal regulations also establish standards for nine contaminants (see Table 6).
The standards include the so-called ‘exceptional quality’ (EQ)
sludges, which meet certain concentration limits (no more than X parts
per million of any of the nine regulated contaminants) as well as pathogen and fly and rodent reduction. With regard to metal concentrations,
sludges and sludge products that fail to meet one or more of those ‘EQ’
pollutant concentrations but which fall below a higher ceiling concentration may be applied, but the applicator is directed to keep track of the
total amount of each metal applied and cease application when a regulatory cumulative pollutant loading limit is reached. Sludge products that
fail to meet one or more of the ‘EQ’ pollutant concentrations but which
fall below the ceiling concentration may still be as long as information on
the acceptable annual pollutant loading rate (APLR) is reached.
344
Aneta Czechowska-Kosacka, Yucheng Cao, Artur Pawłowski
Applies to:
a
All biosolids
that are land
applied
Annual Pollutant Loading
Rate Limits for APLR
Biosolids (kilograms per
hectare per 365-day period)
75
85
3,000
4,300
840
57
75
420
100
7,500
Cumulative Pollutant
Loading Rate Limits for
CPLR Biosolids (kilograms
per hectare)
Arsenic
Cadmium
Chromium
Copper
Lead
Mercury
Molybdenumb
Nickel
Selenium
Zinc
Pollutant Concentration
Limits for EQ and PC
Biosolids
(milligrams per kilogram)2
Pollutant
Ceiling Concentration
Limits for All Biosolids
Applied to Land
(milligrams per kilogram)2
Table 6. Pollutants limits for all land applied sewage sludge [9]
Tabela 6. Limity zanieczyszczeń osadów ściekowych stosowanych na
grunty[9]
41
39
1,200
1,500
300
17
–
420
36
2,800
Bulk
biosolids
and bagged
biosolidsc
41
39
3,000
1,500
300
17
–
420
100
2,800
2.0
1.9
150
75
15
0.85
–
21
5.0
140
Bulk
biosolids
Bagged
biosolidsc
Dry-weight basis
As a result of the February 25, 1994, Amendment to the rule limits for molybdenum were deleted from the Part 503 rule pending EPA reconsideration.
c
Bagged biosolids are sold or given away in a bag or other container.
b
Criteria for Sustainable Disposal of Sewage Sludge
345
4. Criteria for China
In China, the first regulation (Control Standards for Pollutants in
Sludges from Agricultural Use) regarding land application of sewage
sludge was established in l984 by the Ministry of Urban-Rural Construction and Environmental Protection (MURCEP). The regulation set limits
on ten pollutants for sewage sludge used in agriculture. The maximum
allowable concentrations of pollutants in sludges that are applied to land
are presented in Table 6.
In addition, the regulation establishes other requirements:
 annual loading rate of sludge application should not exceed
30 ton/ha,
 if the content of any inorganic chemical contained in sewage sludges
is close to the limit value shown in Table 7, the waste cannot be applied to the same site for more than 20 years,
 sewage sludges should not be used on sandy soil, land with high
ground water level, or conservation area for water resources,
 before land application, sludge must be composted or digested,
 sludge should not be employed on vegetable field or grass lands used
for grazing within 1 year of application,
 when sewage sludge is applied to acid soil, the soil should be treated
with lime,
 sludge loading rate should be reduced if the content of more than one
chemical in sludge reaches the limits,
 if crop growth is affected negatively or harmful chemical content in
crop excesses any standard, sludge application should be stopped.
There have been no regulations for pathogen control for sludge land
application.
346
Aneta Czechowska-Kosacka, Yucheng Cao, Artur Pawłowski
Table 7. Control standards for pollutants in sludges used in agriculture [3]
Tabela 7. Standardowe stężenia zanieczyszczeń w osadach ściekowych
stosowanych w rolnictwie [3]
Parameters
Cadmium
Mercury
Lead
Chromium
Boron
Copper
Zinc
Nickel
Mineral oil
Benzo[a]pyrene
Limit values [mg·kg-1d.m.]
pH < 6.5
5
5
300
600
150
250
500
100
3000
3
pH > 6.5
50
15
1000
1000
150
500
1000
200
3000
3
5. Criteria for Poland
Sewage sludge produced in wastewater treatment plants requires
neutralization not only for practical, but also legal reasons. If possible,
processed sludge should return to the natural environment mainly due to
the content of valuable fertilizing components such as nitrogen or phosphorus, responsible for biomass growth. Agricultural use is recommended for small and medium treatment plants. For large treatment plants, it is
impossible to use sludge in agriculture, as it contains exceeded concentrations of heavy metals.
In the Polish legal system, there is a range of regulations pertaining to sludge management. The basic regulation concerning waste management is the Act on waste of 14th December 2012 (Official Journal, Dz.
U., 2013, item 21) and several regulations which determine the management of sewage sludge in a detailed way. The most important ones include: Regulation of the Polish Minister of Environment of 27th September 2001 on the Waste Catalogue (Official Journal, Dz.U., 2001, No.
112, item 1206); in the case of thermal processing of waste – Regulation
of the Polish Minister of Economy of 21st March 2002 on conditions of
thermal processing of waste (Official Journal, Dz.U., 2002, No. 37, item
Criteria for Sustainable Disposal of Sewage Sludge
347
339); and the Regulation of the Polish Minister of Economy of 8th January 2013 on the criteria and procedures of waste approval for storage at
a waste storage facility of particular type (Official Journal, Dz.U., 2013,
item 38).
One of the most important legal acts regulating sewage sludge
management is the Regulation of the Polish Minister of Environment of
13th July 2010 on municipal sewage sludge (Official Journal, Dz.U.,
2010, No. 137, item 924). This act contains transposed legal regulations
of the European Union. It specifies the conditions which are to be met
while employing municipal sewage sludge in agriculture as well as land
reclamation, including agricultural lands, lands for cultivation of plants
used in compost production, feed production, and plants not intended for
human consumption. Similarly, as in other countries, regulations found in
this act set the limit values for concentrations of seven heavy metals
found in sewage sludge (see Table 8).
Table 8. Limit values for concentrations of heavy metals in municipal sewage
sludge [15]
Tabela 8. Wartości graniczne stężeń metali ciężkich w komunalnych osadach
ściekowych [15]
Heavy metal content [mg·kg-1d.m]
Metals
Cadmium
Copper
Nickel
Lead
Zinc
Mercury
Chromium
in agriculture and the
reclamation of lands for
agricultural purposes
in the reclamation of lands
for non-agricultural
purposes
20
1000
300
750
2500
16
500
25
1200
400
1000
3500
20
1000
348
Aneta Czechowska-Kosacka, Yucheng Cao, Artur Pawłowski
8. Conclusions
Sewage sludge is a sustainable source of phosphorus and potassium
compounds for the growth of biomass. Their application on cultivated land
could be beneficial on condition that the level of pollution does not exceed
the acceptable level, in particular with regard to heavy metals.
Taking into account their possible negative impact on the environment, strict regulations on the content of pollutants in sewage sludge, especially heavy metals, have been established in all the discussed regions.
Bearing in mind both the advantages of the use of sewage sludge
to fertilize crops and the possible risks arising from contaminants,
a number of countries introduced strict regulations governing the use of
sewage sludge to fertilize soil.
Taking into consideration the example of the European Union, the
U.S., Poland and China, it can be concluded on the basis of analysis of
legal regulations in this regard that the use of sewage sludge to fertilize
crops is controlled in an appropriate way in both the developed as well as
the developing countries.
References
1.
Commission of European Communities. Council Directive 86/278/EEC of
4th July 1986 on the protection of the environmental, and in particular of
the soil, when sewage sludge is used in agriculture.
2. Ecimovic T., Haw R, Kondrashin I., Weiler R, Gutierrez F., Vivanco et
al.: Philosophy of the Sustainable Development and the Sustainable Future
of Humankind the Survival of Humanity. Problemy Ekorozwoju – Problems
of Sustainable Development, 9(2), 7–25 (2014).
3. GB4284-84, Control standards for pollutants standards for pollutants in
sewage sludge from agricultural use, 1984.
4. Kelessidis A., Stasinakis A.S.: Comparative study of the methods used for
treatment and final disposal of sewage sludge in European countries.
Waste Management, 12, 1, 201–216, 2012.
5. Kelessidis A., Stasinakis A.S.: Comparative study of the methods used for
treatment and final disposal of sewage sludge in European countries.
Waste Management, 32, 6, 1186–1195, 2012.
6. Konstańczak S.: Theory of Sustainable Development and Social Practice.
Problemy Ekorozwoju – Problems of Sustainable Development. 9, 1, 37–
46, 2014.
Criteria for Sustainable Disposal of Sewage Sludge
349
7. Konarski W.: Mineral Energy Sources and Political Activities: Introduction to Mutual Dependencies and Their Selected Exemplification.Problemy
Ekorozwoju – Problems of Sustianable Development, 9, 1, 63–70, 2014.
8. Krajewski P.: Food Safety and Sustainable Development. Problemy
Ekorozwoju – Problems of Sustianable Development. 9, 2, 79–86, 2014.
9. Land Aplication of sewage Sludge, EPA/831-B-93-002b, December 1994.
10. Metcalf and Eddy, I. Wastewater Engineering: Treatment and Reuse.
Fourth Edition, McGraw-Hill Higher Education, New York 2003.
11. Pawłowska M., Pawłowski L.: Method for elimination of mobile fraction
of heavy metal ions in sewage sludge. Patent nr EP08165555.7 z dnia
2008.09.05.
12. Pawłowski L., Pawłowski A.: Method for producing fuel from sewage
sludge. Patent nr EP09174096.9 z dnia 2009.10.26.
13. Pawłowska M., Siepak J., Pawłowski L., Pleczyński J.: Method for sewage sludge utilisation for intensification of biogas production in refuse collection depot. Patent nr EP08165556.5 z dnia 2008.09.05.
14. Piekarski J., Kogut P., Kaczmarek F., Dąbrowski T.: Biogazownie utylizacyjne jako propozycja utylizacji osadów ściekowych w odniesieniu do
ustawodawstwa polskiego. Rocznik Ochrony Środowiska, Tom 14 (2012).
15. Regulation of the Polish Minister of Environment of 13th July 2010 on municipal sewage sludge (Official Journal, Dz. U., 2010, No. 137, item 924).
16. Singh R.P., Agrawal M.: Potential benefits and risks of land application
of sewage sludge. Waste Management 28, 347–358 (2008).
17. Standards for the use or disposal of sewage sludge, 40 CFR Part 503.
18. Stasinakis A.S., Thomaidis N.S.: Fate and biotransformation of metal and
metalloid species in biological wastewater treatment processes. Critical Reviews in Environmental Science and Technology. 40, 4, 307–364 (2010).
19. Wall G.: Exergy, Life and Sustainable Development, Egzergia, życie
i rozwój zrównoważony. Problemy Ekorozwoju – Problems of Sustianable
Development. 8, 1, 27–41 (2013).
20. Wang X., Chen T., Ge Y., Jia Y.: Studies on land application of sewage
sludge and its limiting factors. J Hazard Mater. 160, 554–558 (2008).
21. Zhang Y., Sheng Li: The Impact of Environmental Preferences on Public
Supporting for the River Ecosystem Restoration Program in China, Problemy
Ekorozwoju – Problems of Sustianable Development. 9, 2, 55–64 (2014).
22. Zhine W., Meijun F., Ikerd J.: Beyond the Dilemma Facing China’s Agriculture – Toward a Chinese Constructive Postmodern Agriculture. Problemy Ekorozwoju. Problems of Sustainable Development. 8 1, 43–56
(2013).
350
Aneta Czechowska-Kosacka, Yucheng Cao, Artur Pawłowski
Kryteria zrównoważonego usuwania osadów ściekowych
Streszczenie
Osady ściekowe są stanowią trwałe źródło związków fosforu i potasu
niezbędnych do wzrostu biomasy. Od ich dostępności dla roślin zależy produkcja żywności dla stale wzrastającej liczby ludności. Do gleby dostarczane są
związki fosforu i potasu w postaci soli pozyskiwanych jako kopaliny. Problem
jednak stanowią szybko wyczerpujące się zasoby minerałów, z których pozyskiwane są wyżej wymienione pierwiastki do produkcji nawozów rolniczych.
W przyszłości ich brak może pogorszyć jakość gleb, co zmniejszy skalę produkcji rolnej. Oznacza to, że podstawowy paradygmat zrównoważonego rozwoju mówiący o konieczności postępowania takiego, aby zapewnić niezbędne
środki do życia obecnym pokoleniom, nie pozbawi przyszłych pokoleń możliwości zabezpieczenia ich potrzeb. Paradygmat ten nakazuje podjęcie wszelkich
działań zdążających do ograniczania eksploatacji naturalnych ich zasobów.
Poszukując innych źródeł zwrócono uwagę na osady ściekowe pochodzące
z biologicznych oczyszczalni ścieków. Osady te zawierają związki fosforu
i potasu, które po odpowiedniej obróbce mogą przyczynić się do spowolnienia
zużycia naturalnych rezerw fosforu i potasu. Zastosowanie osadów ściekowych
na uprawianej ziemi, może być korzystne pod warunkiem, że poziom zanieczyszczeń m.in. metalami ciężkimi nie przekracza dopuszczalnego poziomu.
Biorąc pod uwagę ich możliwy negatywny wpływ na środowisko naturalne oraz
surowe przepisy dotyczące zawartości zanieczyszczeń w osadach, metale ciężkie zostały uwzględnione w prawodawstwie omawianych regionów.
Biorąc pod uwagę zalety wnikające z wykorzystania osadów ściekowych do nawożenia upraw i możliwych zagrożeń wynikających z obecności
w osadach ściekowych niepożądanych zanieczyszczeń, wiele krajów wprowadziło surowe przepisy regulujące wykorzystanie osadów do nawożenia gleby.
Biorąc pod uwagę przykład Europejskiej, USA, Polski i Chin można stwierdzić
na podstawie analizy regulacji prawnych w tym zakresie, że stosowanie osadów
ściekowych do nawożenia gleb jest w pełni kontrolowane zarówno w krajach
rozwiniętych jak również w krajach rozwijających się.
Słowa kluczowe:
zrównoważony rozwój, fosfor, potas, osady ściekowe, uwarunkowania prawne
Keywords:
sustainable development, phosphorus, potassium, sewage sludge,
legal conditions